Effects of emodin and different protein levels on growth and immunity of the blunt snout bream (Megalobrama amblycephala) for in-pond raceway aquaculture systems

The present study aimed to evaluate the effects of emodin and different protein levels on growth-promoting antioxidant capacity and protein utilization of blunt snout bream to in-pond raceway aquaculture systems (IPRS). The experiment was divided into three groups: low protein group (LP) (29% low protein level), high protein group (HP) (32% high protein level), and emodin group (ED) (29% protein level + 0.05% emodin). At 210 days in the late stage of culture, the weight of the ED and HP groups was higher than the LP groups (P < 0.05). Compared with the LP group, the number of hematological parameters (white blood cell, WBC; red blood cell, RBC; hemoglobin, HGB; and hematocrit, HCT), blood antioxidant enzymes (anti-superoxide anion free radical, ASAFA; glutathione peroxidase, GPx; superoxide dismutase, SOD; and nitric oxide, NO) activity in the ED group were significantly increased (P < 0.05), and the serum malondialdehyde (MDA) content were significantly reduced (P < 0.05). Besides, the content of serum triglyceride (TG) and blood antioxidant enzymes (ASAFA, GPx, and SOD) in the HP group were significantly increased compared with the LP group (P < 0.05), and the content of serum Creatinine (CREA) significantly lower than that of the control (P < 0.05). The results of this experiment indicate that emodin and appropriate protein levels can increase the content of antioxidant enzymes, enhance immunity, and promote the growth of M. amblycephala.